This invention relates to surface coatings which impart nonabradable and nonetchable, durable dry lubricity, corrosion resistance and improved permeability characteristics to a substrate and to methods for applying such coatings to a substrate.
Although this invention is primarily directed to the coating of metallic substrates, it is likewise applicable to coatings for application to other suitable substrate materials such as ceramic, graphite and rubber compositions and various mineral surfaces. Furthermore, the metallic substrates employed herein may range from very hard metals having a hardness factor measured on the Rockwell C scale of greater than 40 to soft metals having hardness values measured on the Rockwell B scale.
A wide variety of corrosion-resistant coatings and liquid lubricant compositions and methods for the application of such coatings and lubricants to substrates have been disclosed heretofore. Examples thereof may be found in U.S. Pat. Nos. 3,574,658; 3,754,976; 4,228,670; 4,312,900; 4,333,840; 4,349,444; 4,415,419; 4,552,784; 4,553,417 and 4,753,094. Also, various automotive motor oil lubricant compositions have been disclosed heretofore in publications such as Reick, F. G., "Energy--Saving Lubricants Containing Colloidal PTFE", Journal of the American Society of Lubrication Engineers, Vol. 38, 10, pp. 635-646 (1981); Milton, B. E. et al., "Fuel Consumption and Emission Testing of an Engine Oil Additive Containing PTFE Colloids", Journal of the American Society of Lubrication Engineers, Vol. 39, 2, pp. 105-110 (1983); Guttman, M. and Stotter, A., "The Influence of Oil Additives on Engine Friction and Fuel Consumption", American Society of Lubrication Engineers Preprint No. 84-AM-7D-1 (1984); Reick, F. G., "Variability of PTFE Colloids in Nonaqueous Systems and Lubricating Oils", Journal of the American Society of Lubrication Engineers, Vol. 44, 8, pp. 660-664 (1988); and Bauccio, M. L., "Research and Development with Polytetrafluoroethylene in Automotive Lubricants", a U.S. Army Aviation Systems Command publication, based on a paper presented at the 5th International Colloquium on Additives for Lubricants and Operational Fluids, at the Technische Akademie Esslingen, Esslingen, Germany, on Jan. 14-16, 1986.
Several of the above-noted patents disclose processes for applying coatings to the surface of work pieces by a peening or blasting procedure in which the coating material is applied to the surface by pellets or other shot material impacted at high pressure against the surface of the work piece in order to apply the coating on the pellets or shot to the surface of the work piece.
Other of the above-noted patents and publications disclose fluid compositions for application to substrate surfaces in order to provide lubricant films or coatings on such surfaces. For example, U.S. Pat. No. 4,333,840 discloses a lubricant composition of PTFE in a motor oil carrier diluted with a major amount of a synthetic lubricant having a low viscosity and a high viscosity index. Optionally, a small amount of an oil-soluble molybdenum compound (i.e., about 1%) is included in the composition but, when the percentage of molybdenum compound is excessive relative to the lubricant composition (i.e., in excess of about 1%), the resultant film formed on a metal substrate will be unduly thick and will not provide the described lubricant coating. Also, in U.S. Pat. No. 4,349,444, another hybrid fluid lubricant composition is disclosed in which PTFE particles are uniformly dispersed by a fluorochemical surfactant and are diluted with a major amount of a conventional oil lubricant. The hybrid lubricant includes a small amount (i.e., about 1%) of an oil-soluble organic molybdenum compound. Again, the percentage of molybdenum compound must be small (i.e., about 1%) in order to achieve the results described therein. U.S. Pat. No. 4,415,419 discloses a process for applying a corrosion resistant coating on a sulfide-forming metal substrate such as a sulfided molybdenum surface by cathodic sputtering of a composite lubricant coating of molybdenum disulfide and PTFE onto the sulfided metal layer.
However, none of the prior disclosures have provided products demonstrating the combination of characteristics and properties which are achieved by the coatings and coated products of the present invention, nor do the prior disclosures provide the necessary processes for producing such coated products. Indeed, the need to prolong the wear-life of substrate surfaces such as metal surfaces and to reduce the frictional properties thereof in order to reduce repair and replacement costs has been and continues to be the focus of intensive research and development efforts. Nonetheless, these efforts have achieved only relatively limited success resulting from the use of previously known coatings, paints and lubricants (both wet and dry). Each of the known techniques for treating substrates such as metal surfaces has presented significant problems and drawbacks in regard to the cost, difficulties in application, product properties achieved and the like.
With regard to prior processes for imparting desirable physical properties of polymers to substrate surfaces such as metal surfaces, it has been common to employ fluorocarbon polymers such as tetrafluoroethylene (TFE) sold, for example, under the tradename "Teflon" by E. I. Du Pont de Nemours & Co. (Inc.), as a coating material. Teflon-coated surfaces are known to reduce friction and adhesion, but the Teflon must be applied to the substrate by use of primers such as epoxy and requires high temperatures for application. The coated surface, accordingly, abrades under modest pressure and does not coat evenly or thinly.